Image sensors with column memory repair circuitry

1. An image sensor, comprising: an array of image sensor pixels arranged in rows and columns; a plurality of pixel column lines, each of which is coupled to image sensor pixels arranged along a respective column in the array; analog-to-digital converter circuitry interposed in the plurality of pixel column lines, wherein the analog-to-digital converter circuitry is directly connected to one of the plurality of pixel column lines; and column memory and repair circuitry, wherein the column memory and repair circuitry receives pixel signals from the plurality of pixel column lines and stores the received pixel signals into corresponding column memory circuits in the column memory and repair circuitry, wherein the column memory and repair circuitry implements column-wise repair by selectively bypassing a defective column memory circuit in the column memory circuits, wherein the analog-to-digital converter circuitry is interposed between the image sensor pixels and the column memory and repair circuitry, and wherein the column memory and repair circuitry comprises: a plurality of multiplexers each of which is coupled to a respective one of the column memory circuits; and a scan chain coupled to inputs of the plurality of multiplexers, wherein the scan chain comprises a plurality of flip-flop circuits controlled by a clock signal.

2. The image sensor defined in claim 1 , wherein the scan chain configures the plurality of multiplexers to bypass the defective column memory circuit.

3. The image sensor defined in claim 2 , wherein the column memory and repair circuitry further comprises: a memory repair controller coupled to an input of the scan chain; and programmable read-only memory containing information for configuring the memory repair controller.

4. The image sensor defined in claim 2 , wherein the column memory and repair circuitry further comprises: a plurality of latches, each of which has an input coupled to the scan chain and an output coupled to a respective multiplexer in the plurality of multiplexers.

5. The image sensor defined in claim 1 , further comprising: a column decoder coupled to the column memory circuits.

6. A method of operating an image sensor that includes an array of image sensor pixels arranged in rows and columns, the method comprising: with a selected row of image sensor pixels in the array, outputting pixel signals onto respective column lines; with analog-to-digital converter circuitry directly connected to the column lines, receiving the pixel signals from the column lines and outputting converted pixel signals; with column memory and repair circuitry, receiving the converted pixel signals from the analog-to-digital converter circuitry and implementing column-wise repair by selectively bypassing a defective bit cell column in the column memory and repair circuitry, wherein the column and memory repair circuitry includes a plurality of bit cell columns; in response to determining that multiple bit cell columns in the plurality of bit cell columns are defective, writing a predetermined value into a programmable storage element in the column memory and repair circuitry; storing a read out value in the programmable storage element; and in response to determining that the read out value is not equal to the predetermined value, repairing the plurality of bit cell columns.

7. The method defined in claim 6 , wherein receiving the converted pixel signals from the analog-to-digital converter circuitry comprises receiving the converted pixel signals from respective column lines with at least a portion of the plurality of bit cell columns.

8. The method defined in claim 7 , further comprising: testing the column memory and repair circuitry to determine whether multiple bit cell columns in the plurality of bit cell columns are defective.

9. The method defined in claim 8 , wherein the plurality of bit cell columns includes a spare bit cell column, and wherein repairing the plurality of bit cell columns comprises engaging the spare bit cell column to switch the defective bit cell column out of use.

10. The method defined in claim 8 , wherein the column memory and repair circuitry further includes a scan chain, the method further comprising: using the scan chain to control how the converted pixel signals on the column lines are being routed to the plurality of bit cell columns.

11. The method defined in claim 8 , further comprising: in response to determining that the read out value is equal to the predetermined value, loading a series of logic zeroes into the scan chain; and in response to determining that the read out value is not equal to the predetermined value, repairing the plurality of bit cell columns by loading a series of logic ones followed by a series of zeroes into the scan chain.

12. A system, comprising: a central processing unit; memory; a lens; input-output circuitry; and an imaging device, wherein the imaging device comprises: a pixel array having a plurality of image pixels arranged in rows and columns; column memory circuitry that is coupled to the pixel array and that is configured to implement column-wise memory repair, wherein the column memory circuitry comprises: a plurality of bit cell columns; and multiplexing circuitry, wherein the multiplexing circuitry comprises: a first multiplexer that receives a column signal from the pixel array; and second and third multiplexers that each receive an output of the first multiplexer and that each have an output coupled to a respective bit cell column of the plurality of bit cell columns.

13. The system defined in claim 12 , wherein the multiplexing circuitry bypasses a defective bit cell column in the plurality of bit cell columns.

14. The system defined in claim 13 , wherein the column memory circuitry further comprises: a spare bit cell column that is idle when there are no defective bit cell columns in the plurality of bit cell columns and that is engaged when a defective bit cell column is detected.

15. The system defined in claim 13 , wherein the column memory further comprises: a scan chain that controls how pixel signals from the pixel array are routed to the plurality of bit cell columns.

16. The system defined in claim 15 , wherein the scan chain is configured to store identical values when there are no defective bit cells in the plurality of bit cell columns and to store different values when a defective bit cell column is detected.